Commit 0a9f7780 authored by Dr. Stephen Henson's avatar Dr. Stephen Henson
Browse files

Fix for CVE-2014-0076 

Fix for the attack described in the paper "Recovering OpenSSL
ECDSA Nonces Using the FLUSH+RELOAD Cache Side-channel Attack"
by Yuval Yarom and Naomi Benger. Details can be obtained from:
http://eprint.iacr.org/2014/140

Thanks to Yuval Yarom and Naomi Benger for discovering this
flaw and to Yuval Yarom for supplying a fix.
(cherry picked from commit 2198be34)

Conflicts:

	CHANGES
parent 44f7e399

CHANGES

+9 −0
Original line number Diff line number Diff line
@@ -4,6 +4,15 @@ 


 Changes between 1.0.1f and 1.0.2 [xx XXX xxxx]



  *) Fix for the attack described in the paper "Recovering OpenSSL

     ECDSA Nonces Using the FLUSH+RELOAD Cache Side-channel Attack"

     by Yuval Yarom and Naomi Benger. Details can be obtained from:

     http://eprint.iacr.org/2014/140



     Thanks to Yuval Yarom and Naomi Benger for discovering this

     flaw and to Yuval Yarom for supplying a fix (CVE-2014-0076)

     [Yuval Yarom and Naomi Benger]



  *) Use algorithm specific chains in SSL_CTX_use_certificate_chain_file():

     this fixes a limiation in previous versions of OpenSSL.

     [Steve Henson]

crypto/bn/bn.h

+11 −0
Original line number Diff line number Diff line
@@ -520,6 +520,8 @@ BIGNUM *BN_mod_inverse(BIGNUM *ret, 
BIGNUM *BN_mod_sqrt(BIGNUM *ret,

	const BIGNUM *a, const BIGNUM *n,BN_CTX *ctx);



void	BN_consttime_swap(BN_ULONG swap, BIGNUM *a, BIGNUM *b, int nwords);



/* Deprecated versions */

#ifndef OPENSSL_NO_DEPRECATED

BIGNUM *BN_generate_prime(BIGNUM *ret,int bits,int safe,
@@ -756,11 +758,20 @@ int RAND_pseudo_bytes(unsigned char *buf,int num); 


#define bn_fix_top(a)		bn_check_top(a)



#define bn_check_size(bn, bits) bn_wcheck_size(bn, ((bits+BN_BITS2-1))/BN_BITS2)

#define bn_wcheck_size(bn, words) \

	do { \

		const BIGNUM *_bnum2 = (bn); \

		assert(words <= (_bnum2)->dmax && words >= (_bnum2)->top); \

	} while(0)



#else /* !BN_DEBUG */



#define bn_pollute(a)

#define bn_check_top(a)

#define bn_fix_top(a)		bn_correct_top(a)

#define bn_check_size(bn, bits)

#define bn_wcheck_size(bn, words)



#endif

crypto/bn/bn_lib.c

+52 −0
Original line number Diff line number Diff line
@@ -824,3 +824,55 @@ int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b, 
		}

	return bn_cmp_words(a,b,cl);

	}



/* 

 * Constant-time conditional swap of a and b.  

 * a and b are swapped if condition is not 0.  The code assumes that at most one bit of condition is set.

 * nwords is the number of words to swap.  The code assumes that at least nwords are allocated in both a and b,

 * and that no more than nwords are used by either a or b.

 * a and b cannot be the same number

 */

void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)

	{

	BN_ULONG t;

	int i;



	bn_wcheck_size(a, nwords);

	bn_wcheck_size(b, nwords);



	assert(a != b);

	assert((condition & (condition - 1)) == 0);

	assert(sizeof(BN_ULONG) >= sizeof(int));



	condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;



	t = (a->top^b->top) & condition;

	a->top ^= t;

	b->top ^= t;



#define BN_CONSTTIME_SWAP(ind) \

	do { \

		t = (a->d[ind] ^ b->d[ind]) & condition; \

		a->d[ind] ^= t; \

		b->d[ind] ^= t; \

	} while (0)





	switch (nwords) {

	default:

		for (i = 10; i < nwords; i++) 

			BN_CONSTTIME_SWAP(i);

		/* Fallthrough */

	case 10: BN_CONSTTIME_SWAP(9); /* Fallthrough */

	case 9: BN_CONSTTIME_SWAP(8); /* Fallthrough */

	case 8: BN_CONSTTIME_SWAP(7); /* Fallthrough */

	case 7: BN_CONSTTIME_SWAP(6); /* Fallthrough */

	case 6: BN_CONSTTIME_SWAP(5); /* Fallthrough */

	case 5: BN_CONSTTIME_SWAP(4); /* Fallthrough */

	case 4: BN_CONSTTIME_SWAP(3); /* Fallthrough */

	case 3: BN_CONSTTIME_SWAP(2); /* Fallthrough */

	case 2: BN_CONSTTIME_SWAP(1); /* Fallthrough */

	case 1: BN_CONSTTIME_SWAP(0);

	}

#undef BN_CONSTTIME_SWAP

}

crypto/ec/ec2_mult.c

+16 −11
Original line number Diff line number Diff line
@@ -208,11 +208,15 @@ static int gf2m_Mxy(const EC_GROUP *group, const BIGNUM *x, const BIGNUM *y, BIG 
	return ret;

	}





/* Computes scalar*point and stores the result in r.

 * point can not equal r.

 * Uses algorithm 2P of

 * Uses a modified algorithm 2P of

 *     Lopez, J. and Dahab, R.  "Fast multiplication on elliptic curves over 

 *     GF(2^m) without precomputation" (CHES '99, LNCS 1717).

 *

 * To protect against side-channel attack the function uses constant time swap,

 * avoiding conditional branches.

 */

static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,

	const EC_POINT *point, BN_CTX *ctx)
@@ -246,6 +250,11 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, 
	x2 = &r->X;

	z2 = &r->Y;



	bn_wexpand(x1, group->field.top);

	bn_wexpand(z1, group->field.top);

	bn_wexpand(x2, group->field.top);

	bn_wexpand(z2, group->field.top);



	if (!BN_GF2m_mod_arr(x1, &point->X, group->poly)) goto err; /* x1 = x */

	if (!BN_one(z1)) goto err; /* z1 = 1 */

	if (!group->meth->field_sqr(group, z2, x1, ctx)) goto err; /* z2 = x1^2 = x^2 */
@@ -270,16 +279,12 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, 
		word = scalar->d[i];

		while (mask)

			{

			if (word & mask)

				{

				if (!gf2m_Madd(group, &point->X, x1, z1, x2, z2, ctx)) goto err;

				if (!gf2m_Mdouble(group, x2, z2, ctx)) goto err;

				}

			else

				{

			BN_consttime_swap(word & mask, x1, x2, group->field.top);

			BN_consttime_swap(word & mask, z1, z2, group->field.top);

			if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err;

			if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err;

				}

			BN_consttime_swap(word & mask, x1, x2, group->field.top);

			BN_consttime_swap(word & mask, z1, z2, group->field.top);

			mask >>= 1;

			}

		mask = BN_TBIT;